July 11, 2013

New Blue Exoplanet Shares Only Its Color With Earth

Using imagery from the Hubble Space Telescope, astronomers have determined that a planet orbiting a star close to our solar system has a deep azure blue color when seen from space, much like Earth.

The international team that made the discovery noted similarities between these two planets likely end at their color, as the exoplanet HD 189733b is being described as a gas giant with thousand degree temperatures and violent winds in its atmosphere.

Only 63 light years from Earth, HD 189733b is referred to as a "hot Jupiter," a class of planets that resemble our solar system's own gas giants but which orbit much closer to their sun than Saturn or Jupiter. It has been a recent planet of interest for Hubble and other telescopes.

"This planet has been studied well in the past, both by ourselves and other teams," said Frederic Pont of the University of Exeter in the United Kingdom and a Hubble program leader. "But measuring its color is a real first - we can actually imagine what this planet would look like if we were able to look at it directly."

According to the team's report in Astrophysical Journal Letters, they were able to use the planet's albedo, or light reflected off its surface, to determine its color. The planet's reflected light was isolated from the light of its star using Hubble's Space Telescope Imaging Spectrograph (STIS) to watch the entire system before, during and after the planet passed behind its star. When the planet passed behind the star, its reflected light was blocked from view, changing the dynamics of the entire system's light being seen from Earth.

"We saw the brightness of the whole system drop in the blue part of the spectrum when the planet passed behind its star," explained co-author Tom Evans of the University of Oxford. "From this, we can gather that the planet is blue, because the signal remained constant at the other colors we measured."

According to the team, the planet's color comes not from blue oceans, but rather from a muddled, chaotic atmosphere filled with silicate particles which disperse blue light. The Hubble observations allowed the scientists to confirm previous theories about the planet's blue color.

The colors of gaseous planets like Jupiter and Venus are due to unknown atmospheric particles. Earth, on the other hand, appears blue because the oceans strongly absorb red and green light and reflect the bluish hue of our sky, the scientists said.

"It's difficult to know exactly what causes the color of a planet's atmosphere, even for planets in the Solar System," Pont said. "But these new observations add another piece to the puzzle over the nature and atmosphere of HD 189733b. We are slowly painting a more complete picture of this exotic planet."

First discovered in 2005, HD 189733b is one of a number of hot Jupiters known to exist throughout the Universe. The planet is relatively close to Earth and unlike anything else in our own Solar System, making it an attractive object of study for researchers.